The equation of state (EOS) used in the present calculations is composed of two
parts which apply to different regions. The first part of the EOS is used for the
degenerate, completely ionized interior of the white dwarf. In this region, we use
the EOS tables provided by Lamb ([1]}). For a given chemical composition the
needed values are obtained by two-dimension, four-point Aitken-Lagrange interpolation
in terms of variables \(\lg P\)  and \(\lg T\) . For a specific C/O mixture, they are
obtained by interpolation between the carbon and oxygen tables using the additive
volume technique of Fontaine et al. ([2]}). The second part of the EOS is used
for the partial ionized envelope where non-ideal effect is important. We use the
Saumon et al. ([3]}) EOS for hydrogen and helium mixtures. The new EOS
include some new physical treatments of partial ionization caused by pressure and
temperature. Mixtures of hydrogen and helium are also obtained by the additive
volume technique.
